This invention relates to an apparatus for data transfer with a rotating data storage disk such as, typically, a flexible magnetic disk commonly known as floppy disk and, more particularly, to a flexible magnetic disk drive suitable for connection as a peripheral to a personal computer via a universal serial bus (USB) interface. Still more particularly, the invention concerns how to reduce the maximum current requirement of such a disk drive at a minimal sacrifice of the seek speed, specifically dealing with the interrelated control of the current consumptions of a disk drive motor and a transducer positioning motor.
There recently have been introduced to the market the personal computers that have what is called a universal serial bus (USB) port for connection to a set of peripherals via serial USB interfaces. A plurality of peripherals, each with a USB interface, may be connected to what is termed a USB hub via separate USB cables and thence to the USB port of the computer via a single USB cable. USB connections are generally acknowledged to greatly enhance the utility and versatility of personal computer systems.
There has, however, been a problem left unsolved in connection with the USB interfacing of personal computers and peripherals. The power supply buses of USB cables are capable of carrying a current of no more than 500 milliamperes, a prerequisite demanding that the maximum current requirement of each computer peripheral be within that limit. More conventional flexible magnetic disk drives, for example, that are not designed for USB interfacing have a maximum current requirement ranging from 600 to 800 mA. Difficulties have therefore been experienced in designing disk drives, among other peripherals, that meet the current carrying capacity of USB cables.
The difficulties have been caused for the most part by the large current consumptions of a disk drive motor and a transducer positioning motor, both invariably incorporated in a disk drive to enable the transducers to access the individual storage locations on the disk for reading or writing. The combined current requirement of the two motors occupies a very substantive percentage of the total current requirement of the disk drive.
A conventional solution to this problem has been to make the current consumption of the transducer positioning motor less than that in universal disk drives that are not designed for USB interfacing with computers. The total current requirement of the USB interfaced disk drive has thus been made not to exceed the 500 mA limit at the sacrifice of the seek speed.
In a flexible magnetic disk drive for use with interchangeable disks, which vary considerably in weight, the current consumption of the disk drive motor is subject to change in the range of approximately 100 to 300 mA according to the particular weight of each disk it is driving. The current consumption of the transducer positioning motor, on the other hand, has been so predetermined that the total current consumption of the disk drive, including the maximum level of current consumption of the disk drive motor for disks of the heaviest weight class, may fall within the limit.
Consequently, when a disk of less than the heaviest weight class is loaded, the current consumption of the disk drive motor falls below the maximum level, but that of the positioning motor has so far been left unchanged. An unutilized margin has thus been created between the 500 mA limit of USB cables and the total current consumption of the disk drive whenever a disk of less than the prescribed maximum weight class is loaded therein.
It is therefore an object of this invention to make utmost use of the margin, so far wasted, between the 500 mA limit of USB cables and the total current consumption of the disk drive when a disk of less than the prescribed maximum weight class is being driven.
A more specific object of the invention is to make the seek speed of a USB interfaced disk drive or like computer peripheral higher in inverse proportion to the magnitude of the current being consumed by a disk drive motor, by taking advantage of the fact the current consumption of the disk drive motor lessens when it is driving disks of less than the prescribed maximum weight class.
Stated in brief, the present invention provides a data storage apparatus for use with interchangeable data storage disks of potentially different weights, comprising a disk drive motor for imparting rotation to a data storage disk loaded in the apparatus, and a positioning motor for moving a transducer across track turns on the disk. Also included are current detector means for detecting the magnitude of an electric current being consumed by the disk drive motor when the latter is driving the loaded data storage disk at a prescribed speed, current control means for controlling the magnitude of a current supplied to the positioning motor in inverse proportion to the detected magnitude of the current being consumed. by the disk drive motor, and speed control means for varying the speed of rotation of the positioning motor in inverse proportion to the detected magnitude of the current being consumed by the disk drive motor.
In a preferred embodiment the disks to be interchangeably loaded n the apparatus are classified into three weight classes, heavy, average, and light. Which of these weight classes each disk belongs to is determined by the current detector means by detecting the current consumption of the disk drive motor driving that disk, the current consumption of the disk drive motor being proportional to the disk weight. In response to the resulting output from the current detector means, the current control means determines the current supplied to the positioning motor in one of three predetermined levels, and the speed control means determines the rotational speed of the positioning motor in one of three predetermined levels.
The seek speed is therefore the same as heretofore for disks of the heavy weight class, but definitely higher for disks of the average weight class, and even higher for disks of the light weight class. These improvements in seek speed are accomplished with the total current consumption of the disk drive motor and the positioning motor maintained no more than heretofore for disks of all the weight classes.
The classification of the disks into several weight categories, and the provision of as many seek speeds each suiting one weight category, are, however, not an essential feature of the instant invention. The seek speed may be varied infinitely for each disk of a particular weight, as also taught herein.
The above and other objects, features and advantages of this invention and the manner of achieving them will become more apparent, and the invention itself will best be understood, from a study of the following description and attached claims, with reference had to the accompanying drawings showing the preferred embodiments of the invention.